1. Field of the Invention
The present invention is directed to a lifting device used in the repair of concrete roads which lifts out damaged sections of the concrete that have been cut from the surrounding road.
2. Background of the Invention
Referring to the section of road shown in the drawings, a common practice for repairing damaged sections of concrete slabs 2 forming the road is to cut out and remove a damaged section 3 and pour a concrete patch in the remaining hole. The area around lateral control joints 5 formed in the slabs 2 which have degraded over time are areas that are commonly in need of repair. The concrete slab 2 forming a road is typically poured as a generally continuous slab. The slab may be approximately nine to twelve inches thick. Saw cuts are then cut into the slab 2, commonly about one third of the thickness of the pavement, to provide an area of weakness at which cracks will naturally form in the slab 2. Longitudinal joints 6 are formed longitudinally along the slab 2 to separate lanes that are typically twelve feet wide. Lateral control joints 5 are formed laterally across the slab 2 typically approximately fifteen feet apart.
Damage at the lateral control joints 5, typically starts with chipping and spawling of the edges of the joint 5, forming a small depression which then grows as tires continuously pound against the defect and water seeps into the cracks therein and freezes further expanding the defects. Over time cracks will also form extending outward from the joint 5. In addition, cracks may form across the slab between control joints 5 which is more common when the spacing between control joints 5 is increased, such as for example thirty foot spacings.
A typical procedure for repairing a slab having a degraded control joint 5 is to cut out and remove a specified amount of the concrete slab 2 on either side of the degraded joint 5. The width of the slab to be removed may vary depending on specifications established by the jurisdiction in charge of the road repair. Typically, the jurisdiction or owner will specify removing at least two to three feet of the concrete slab 2 on either side of the joint 5 and in some cases up to approximately five feet on either side of the joint 5. The portion of the slab 2 removed may be referred to as the damaged section or fragmented section 3. The fragmented section 3 typically includes at least two fragments 9, but may further fragment into additional fragments 9 due to cracks radiating outward from the joint 5.
In repairs, cuts 11 are made through the concrete slab outward from the crack on both sides the distance specified. Holes 13 are then drilled in the fragmented section 3 to be removed with at least one hole 13 per fragment 9 to be removed. Expansion pins are then inserted into the holes and expanded to lock the pins in the holes. The holes 13 are drilled to a size adapted to receive a non-expanded pin which is typically between two to three inches in diameter. After the pins are inserted in the hole 13, the pins are expanded until the diameter of the pin equals the diameter of the hole 13 in which it is inserted wedging the pin in place and securing the slab to the pin. The pins are connected together by a harness that is then lifted with an excavator or the like to lift the pins and the fragmented section 3 connected thereto from the rest of the concrete roadway or slab 2.
Great care must be taken when lifting the damaged section 3 so as not to chip the edges of the concrete slab 2 on either side of the damaged section 3 as it is lifted. Roadway repair specifications or guidelines often specify that if the edge of the slab adjacent the removed damaged section 3 is chipped or spalled, the contractor has to make another cut to remove the damaged edge and create a new clean edge. Lifting a cracked and fragmented section 3 using a harness connected to locking pins without the load shifting and causing damage to the edge remaining slab is very difficult requiring additional labor to help guide the damaged section from between the adjacent sections of the remaining slab and at a very slow pace. Even then, the crew may not be able to prevent damage due to shifting of the load.
It is known to bolt frames to sections of a fragmented slab to stabilize the fragments prior to lifting the fragments from the road. See for example, U.S. Pat. No. 7,448,176 to Drake and U.S. Pat. No. 6,752,566 to Smith. However, the system disclosed in the Smith '566 patent relies on the use of cables or straps connected between the frame and an overhead crane or the like for lifting the stabilized slab from the adjacent sections of the concrete road which, as discussed, can still result in damage to the edges of the adjacent road. The Drake '176 patent appears to be silent on how the stabilized slabs are lifted from the concrete road.
There remains a need for a system for stabilizing and removing damaged and fragmented sections of a concrete slab in an efficient manner without damaging the edges of the slab adjacent to the sections removed. There further remains a need for such a system which can be operated by a minimal number of operators to reduce the labor costs in repairing damaged roads and slabs.